Back in college, frat parties baffled me. It wasn't the sticky dancefloors or the live-goldfish-swallowing or even the attempts to re-create the exclusivity of a velvet-roped NYC club in the middle of Ohio with lists and bouncers and strict ratios of guys to girls -- I kind of understood all that. What I always wondered about was how much people drank, and the way in which they did it. It always seemed to be a competition, with bragging rights awarded to the most copious drinkers, the most raging hangovers, the most ridiculous half-remembered antics from the night before.

But why? Isn't drinking this kind of intensely personal activity with pleasures that by definition don't extend much beyond your own brain? It makes you feel loose and loopy. Who cares if other people know how much you drank to achieve that effect? And yet it's a major part of frat culture, and drinking culture at large. And a recent study reported in Scientific American may help answer my long-burning why.

Spend any time in a bar, and sooner or later you'll hear, "I'll have what she's having." It sounds like a bad pickup line, but there may be an actual biological basis for this kind of alcohol copycat behavior. Because scientists have found that having the gene for a certain dopamine receptor could predispose you to being influenced by the sight of other people drinking.

Volunteers were ushered into a lab set up to look like a pub. They were asked to do some busywork, then told that during the break they should help themselves to some adult beverages. While they watched, shills planted by the scientists immediately liquored up. The study subjects were then tracked to see how much they drank after watching others toss "˜em back. When the plants could be seen having just one drink, all the subjects drank similar amounts. But when the plants had at least three drinks, some participants drank twice as much as others.

It's a much weirder answer than I ever would've thought: why is there peer pressure to drink? Because, possibly, certain people are genetically predisposed to drink more by the sight of other people drinking. In a fraternity environment, I imagine this would quickly lead to a cascade effect of the kind you could witness any Friday or Saturday night on frat row, the alcoholic equivalent of facing two mirrors at one another (except instead of retreating into infinity, the drinkers retreat into an unconscious stupor).

How influenced are you by the sight of other people drinking?